Low cost compact size single stage high power factor circuit for discharge lamps

Abstract

The present application claims a compact low cost topology solution of a ballast for a discharge lamp that can provide both high power factor and low total harmonic distortion with fewer components than prior art. The topology provides the feature of a low crest factor and quick start that increase both the lamp life and the number of starts for the product. By using Bipolar Junction Transistor instead of Field Effect Transistor as the main switches and also a lower value electrolytic, the cost and size are considerably reduced.

1. A ballast circuit or driving a discharge lamp, comprising:
 a power input operative to receive an AC input signal; 
 a rectifier comprising a rectifier input including first and second rectifier input terminals coupled with the power input, a rectifier output coupled to first and second terminals of a DC bus, and at least one rectifier diode coupled between the rectifier input and the rectifier output and operative to convert AC power at the rectifier input to provide DC power to the DC bus; 
 an inverter including first and second Bipolar Junction Transistors (BJTs) coupled in series between the first and second DC bus terminals, the first and second BJTs connected to one another at an inverter central node; 
 a transformer with a primary winding coupled between the inverter central node and a first lamp connection, and first and second secondary windings; 
 a driver circuit including the first and second secondary windings of the transformer, the first secondary winding of the transformer being coupled with a base terminal of the first BJT, and the second secondary winding of the transformer being coupled with a base terminal of the second BJT, the driver circuit operative to drive the first and second BJTs in alternating fashion to provide a high frequency AC inverter output signal at the inverter central node; 
 a first capacitance coupled in series between the first lamp connection and the first rectifier input terminal; and 
 a second capacitance coupled in series between a second lamp connection and the second rectifier input terminal. 
 
     
     
       2. The ballast circuit of  claim 1 , where the primary winding senses a lamp current and a resonant current of the first capacitance. 
     
     
       3. The ballast circuit of  claim 2 , further comprising a third capacitance coupled in parallel across the at least one rectifier diode of the rectifier. 
     
     
       4. The ballast circuit of  claim 3 , where the at least one rectifier diode comprises an anode connected to the first rectifier input terminal and a cathode connected to the first DC bus terminal, and where the third capacitance is connected between the first rectifier input terminal and the first DC bus terminal. 
     
     
       5. The ballast circuit of  claim 4 , where the rectifier s a full bridge rectifier comprising four rectifier diodes, where a first rectifier diode comprises an anode connected to the first rectifier input terminal and a cathode connected to the first DC bus terminal, and where the third capacitance is connected between the first rectifier input terminal and the first DC bus terminal. 
     
     
       6. The ballast circuit of  claim 1 , further comprising a third capacitance coupled in parallel across the at least one rectifier diode of the rectifier. 
     
     
       7. The ballast circuit of  claim 6 , where the at least one rectifier diode comprises an anode connected to the first rectifier input terminal and a cathode connected to the first DC bus terminal, and where the third capacitance is connected between the first rectifier input terminal and the first DC bus terminal. 
     
     
       8. The ballast circuit of  claim 1 , where the rectifier is a full bridge rectifier comprising four rectifier diodes, where a first rectifier diode comprises an anode connected to the first rectifier input terminal and a cathode connected to the first DC bus terminal, further comprising a third capacitance is connected in parallel with the first rectifier diode. 
     
     
       9. A ballast circuit for driving a discharge lamp, comprising:
 a power input operative to receive an AC input signal; 
 a rectifier comprising a rectifier input including first and second rectifier input terminals coupled with the power input, a rectifier output coupled to first and second terminals of a DC bus, and at least one rectifier diode coupled between the rectifier input and the rectifier output and operative to convert AC power at the rectifier input to provide DC power to the DC bus; 
 an inverter including first and second Bipolar Junction Transistors (BJTs) coupled in series between the first and second DC bus terminals, the first and second BJTs connected to one another at an inverter central node; 
 an inductance coupled between the inverter central node and a first lamp connection; 
 a transformer with a primary winding coupled between second and third lamp connections, and first and second secondary windings; 
 a driver circuit including the first and second secondary windings of the transformer, the first secondary winding of the transformer being coupled with a base terminal of the first BJT, and the second secondary winding of the transformer being coupled with a base terminal of the second BJT, the driver circuit operative to drive the first and second BJTs in alternating fashion to provide a high frequency AC inverter output signal at the inverter central node; 
 a first capacitance coupled in series between the first lamp connection and the first rectifier input terminal; and 
 a second capacitance coupled in series between a fourth lamp connection and the second rectifier input terminal. 
 
     
     
       10. The ballast circuit of  claim 9 , further comprising a third capacitance coupled in parallel across the at least one rectifier diode of the rectifier. 
     
     
       11. The ballast circuit of  claim 10 , where the at least one rectifier diode comprises an anode connected to the first rectifier input terminal and a cathode connected to the first DC bus terminal, and where the third capacitance is connected between the first rectifier input terminal and the first DC bus terminal. 
     
     
       12. The ballast circuit of  claim 11 , where the primary winding is connected in series with both filaments of a connected lamp. 
     
     
       13. The ballast circuit of  claim 11 , where the rectifier is a full bridge rectifier comprising four rectifier diodes, where a first rectifier diode comprises an anode connected to the first rectifier input terminal and a cathode connected to the first DC bus terminal, and where the third capacitance is connected between the first rectifier input terminal and the first DC bus terminal. 
     
     
       14. The ballast circuit of  claim 10 , where the primary winding is connected in series with both filaments of a connected lamp. 
     
     
       15. The ballast circuit of  claim 14 , where the rectifier is a full bridge rectifier comprising four rectifier diodes, where a first rectifier diode comprises an anode connected to the first rectifier input terminal and a cathode connected to the first DC bus terminal, and where the third capacitance is connected between the first rectifier input terminal and the first DC bus terminal. 
     
     
       16. The ballast circuit of  claim 10 , where the rectifier is a full bridge rectifier comprising four rectifier diodes, where a first rectifier diode comprises an anode connected to the first rectifier input terminal and a cathode connected to the first DC bus terminal, and where the third capacitance is connected between the first rectifier input terminal and the first DC bus terminal. 
     
     
       17. The ballast circuit of  claim 9 , where the rectifier is a full bridge rectifier comprising four rectifier diodes, where a first rectifier diode comprises an anode connected to the first rectifier input terminal and a cathode connected to the first DC bus terminal, further comprising a third capacitance is connected in parallel with the first rectifier diode. 
     
     
       18. The ballast circuit of  claim 17 , where the primary winding is connected in series with both filaments of a connected lamp. 
     
     
       19. The ballast circuit of  claim 9 , where the primary winding is connected in series with both filaments of a connected lamp. 
     
     
       20. A ballast circuit for driving a discharge lamp, comprising:
 a power input operative to receive an AC input signal; 
 a rectifier comprising a rectifier input including first and second rectifier input terminals coupled with the power input, a rectifier output coupled to first and second terminals of a DC bus, and at least one rectifier diode coupled between the rectifier input and the rectifier output and operative to convert AC power at the rectifier input to provide DC power to the DC bus; 
 an inverter including first and second Bipolar Junction Transistors (BJTs) coupled in series between the first and second DC bus terminals, the first and second BJTs connected to one another at an inverter central node, the inverter central node coupled with a first lamp connection; 
 a driver circuit operative to drive the first and second BJT's in alternating fashion to provide a high frequency AC inverter output signal at the inverter central node; 
 a first capacitance directly connected in series between the first lamp connection and the first rectifier input terminal; and 
 a second capacitance directly connected in series between a fourth lamp connection and the second rectifier input terminal.